Some 'setting'....? (News page does no work)

I just found out I cannot 'live stream' two of my news pages. [Firefox does] The news organization has a list of 'supported' browsers. Vivaldi is not on the list, so I E-Mailed them and told them I needed Vivaldi added. If they do it or not, anybody's guess....

In the meantime....maybe there is some setting [or combination of commands] that will give me a Work-Around ?

@mister-bill
As Oblivion said a user agent switcher to fake Vivaldi's id to the website should do the trick.
You can get one from chrome web store (link below) as an extension.
Install one -> go to the website -> click the extension icon -> select a browser as which Vivaldi should cloak itself (chrome/firefox/whatever) and reload the page -> hopefully this works now.

Never the less it would be nice to know if this works and where this happens in case somebody else has the same problem with those sites so we can provide a solution right away.